Proton implanted VCSEL's for 3 Gb/s data links

Transverse single-mode and multimode intensity modulated butt-coupled InGaAs vertical cavity surface emitting lasers (VCSEL)s are investigated as a light source for optical fiber communication systems. Data transmission at 3 Gb/s with a bit error rate (BER) of less than 10 ^-11 is reported for both 4.3 km of standard fiber, as well as 0.5 km of multimode graded-index fiber, 10-μm active diameter single-mode VCSELs are shown to have lower mode competition noise requiring 3 dB and 6 dB less power at the front end receiver at a BER of 10^-11 compared to 19-μm and 50-μm active diameter devices, respectively. In data transmission with multimode VCSELs, the dispersion penalty is lower than for single-mode sources since the noise at the receiver is mainly determined by transmitter-mode competition noise     

40-GHz polymer electrooptic phase modulators

A broad-band high-frequency traveling wave electrooptic phase modulator made from stable nonlinear optical polymers has been tested. Using a 1.319-μm light source, single-mode operation was achieved with high-input optical power, resulting in improved modulation depths and signal-to-noise ratios. The high-frequency optical modulation was observed up to 40 GHz using external microwave mixers. Direct optical-heterodyne detection of electrooptic phase modulation has also been demonstrated with high sensitivity at 40 GHz. The devices were tested with 10⁵ W/cm² power density for 21 hours, and have showed no observable decay in nonlinearity     

1.55-μm Ce,Er:ZBLAN fiber laser operation under 980-nm pumping:experiment and simulation

Fiber laser operating property at 1.55-μm band in a newly developed Ce,Er:ZBLAN fiber by a continuous-wave laser diode pumping at 980 nm is presented. The output characteristics of the Ce,Er:ZBLAN fiber laser system are analyzed in detail based on the rate equations model by taking into account the energy transfer between Ce³⁺ and Er ³⁺ ions, as well as the upconversion mechanisms. The promotion role of the Ce in the erbium-doped ZBLAN for the 1.55-μm band fiber laser operation has been realized     

5 Gb/s optical soliton transmission experiment using Ramanamplification for fiber-loss compensation

Optical soliton transmission of 5 Gb/s over a 23-km amplification spacing using a gain-switched 1.55-μm distributed feedback laser diode and Ti:LiNbO₃ intensity modulator is discussed. An Er ⁺-doped fiber amplifier, pumped by 1.45- and 1.48-μm laser diodes, is employed for achieving intense optical pulses. Transmission fiber-loss is completely compensated for by Raman amplification using by 1.45- and 1.48-μm laser-diode pumping. A bit error rate (BER) of 2×10^-10 has been obtained     

Er3+-doped fiber amplifier pumped by 0.98 μm laserdiodes

The performance of an Er³⁺-doped fiber amplifier pumped by 0.98 μm InGaAs laser diodes (LDs) is reported. By using a fiber with low Er³⁺ content and optimizing the fiber length, a maximum signal gain of 37.8 dB at 30-mW pump power was realized at a signal wavelength of 1.536 μm. A maximum gain coefficient of 1.9 dB/mW at 14 mW pump power was achieved. It was found that the fiber amplifier pumped by the 0.98-μm LDs is twice as efficient as that pumped by 1.48-μm LDs, from the viewpoint of both required fiber length and the attained gain     

Low-loss 1.3-μm MQW electroabsorption modulators forhigh-linearity analog optical links

Low-loss InAsP-GaInP multiquantum-well electroabsorption waveguide modulators have been developed for transmitting microwaves as subcarriers over optical fibers. The fiber-to-fiber insertion loss is only 5 dB at 1.32-μm wavelength. The electrooptic slope efficiency of an 185-μm-long 11-GHz bandwidth device is equivalent to a Mach-Zehnder modulator with a V_π of 2.2 V. The linearity performance was characterized for a test link without any form of amplification. A RF-to-RF link efficiency of -25.5 dB, noise figure of 27 dB and suboctave spurious-free dynamic range of 114 dB.Hz^4/5 have been achieved with 16 mW input optical carrier power. The measured 3-dB electrical bandwidth exceeds 20 GHz for a 90-μm-long device     

An efficient low voltage, high frequency silicon CMOS lightemitting device and electro-optical interface

A silicon light emitting device was designed and realized utilizing a standard 2-μm industrial CMOS technology design and processing procedure. The device and its associated driving circuitry were integrated in a CMOS integrated circuit and can interface with a multimode optical fiber. The device delivers 8 nW of optical power (450-850 nm wavelength) per 20-μm diameter of chip area at 4.0 V and 5 mA. The device emits light by means of a surface assisted Zener breakdown process that occurs laterally between concentrically arranged highly doped n⁺ rings and a p⁺ centroid, which are all coplanarly arranged with an optically transparent Si-SiO₂ interface. Theoretical and experimental determinations with capacitances and series resistances indicate that the device has an intrinsic high-frequency operating capability into the near gigahertz range     

Simultaneous amplification and channel equalization using Ramanamplifier for 30 channels in 1.3-μm band

A new technique is proposed to simultaneously amplify signals and equalize power unbalance caused by Raman-induced crosstalk among optical channels in the 1.3-μm band. The crosstalk is induced in GeO₂ -doped silica fibers due to the Raman-gain coefficient with a positive slope below the peak-frequency shift of 440 cm^-1. Highly doped GeO₂ silica fiber, however, shows a negative slope across the band between 440 cm^-1 and 490 cm^-1. We propose expansion of the Raman-gain band with a negative slope over the bandwidth of 150 cm^-1 using multiple pumps. Utilizing the negative gain slope of the proposed band, simultaneous amplification and power equalization was theoretically demonstrated for 30 channels in the 1.310-1.345 μm region without external filters     

A highly efficient two-stage Er3+-doped optical fiberamplifier employing an optical gate to effectively reduce ASE

Highly efficient amplification of ultrashort optical pulses is demonstrated with a two-stage Er³⁺-doped optical fiber amplifier that includes an optical gate to efficiently reduce amplified spontaneous emission (ASE) generated from the first Er³⁺-doped fiber. A gain of 49 dB, an amplified peak power 0f 105 W, and 1.05 nJ pulse energy are achieved for 2-Mb/s, 10-ps pulses at a total pumping power of 90 mW from 1.48-μm LDs     

Laser diode-pumped holmium-doped fluorozirconate glass fiber laserin the green (λ~544-549 nm): power conversion efficiency, pumpacceptance bandwidth, and excited-state kinetics

The green (544-549 nm) Ho-doped fluorozirconate (ZBLAN) glass fiber laser, pumped in the red (λ~6;15 nm) by a high-power (~30 mW) InGaAlP laser diode or a ring dye-laser, has been characterized with regard to power conversion efficiency, fiber core-diameter and length, cavity output coupling, and pump acceptance bandwidth. Fibers doped with ~1200 ppm (by weight) of Ho and having core diameters of 1.7, 3, and 11 μm, and lengths ranging from 12.5 to 86 cm, have been studied in Fabry-Perot resonators having output couplings ranging from 1.545 to 96%. For a 1.7-μm core-diameter fiber, 21 cm in length, the threshold-launched pump power for the diode-pumped fiber laser is 1.9 and 3.5 mW for cavity output couplings of 1.5% and 24%, respectively. These values are the lowest for any upconversion-pumped fiber laser reported to date. Also, the noise and threshold-pumping power properties of the diode-pumped fiber laser are superior to those for its dye-laser-pumped counterpart. The highest laser slope efficiency (>22% with respect to launched pump power) was measured for a 3-μm core-diameter fiber and a cavity output coupling of 24%. The spectral interval over which the launched threshold pump power for this laser is <10 mW is almost 20 nm (637-656 nm). Studies of the fiber laser waveform as a function of pump power reveal competition for population between the ⁵S² and ⁵F₄ states and among the Stark sublevels of the ⁵F₄ manifold. Also, measurements of the output power on individual laser lines of the ⁵F₄, ⁵S₂→ ⁵I₈ (ground) transitions of Ho³⁺:ZBLAN as a function of pump power demonstrate the existence of a loss mechanism at the fiber laser wavelength, presumably due to absorption from ground or the ⁵I_y, ⁶S₂ or ⁵F₄ excited states of the ion     

Ultralow-threshold-current lasing in inversion channel lasers

A new regime of semiconductor laser operation was observed in quantum-well inversion channels of double heterostructure optoelectronic switches. The quantum-well active region operated with substantial excess negative charge imbalance due to the proximity of a high-density depleted donor charge sheet. Threshold current densities as low as 15 A/cm² in as-cleaved 400-μm-long devices were measured, and unusual high-frequency operation under low power operation was observed. These qualities may be of great significance for optical interconnections and optoelectronic integrated circuits     

27-GHz bandwidth high-speed monolithic integrated optoelectronicphotoreceiver consisting of a waveguide fed photodiode and anInAlAs/InGaAs-HFET traveling wave amplifier

A monolithic integrated photoreceiver for 1.55-μm wavelength has been designed for operation in a 20-Gb/s synchronous digital hierarchy system (SDH/SONET), based on a new integration concept. The optoelectronic integrated circuit (OEIC) receiver combines a waveguide-integrated PIN-photodiode and a traveling wave amplifier in coplanar waveguide layout with four InAlAs/InGaAs/InP-HFETs (0.7-μm gate length). The receiver demonstrates a bandwidth of 27 GHz with a low frequency transimpedance of 40 dBΩ. This is, to our knowledge, the highest bandwidth ever reported for a monolithic integrated photoreceiver on InP. Furthermore, a receiver sensitivity of -12 dBm in the fiber (20 Gb/s, BER=10^-9) and an overall optical input dynamic range of 27 dB is achieved. Optical time domain multiplex (TDM) system experiments of the receiver packaged in a module show an excellently shaped eye pattern for 20 Gb/s and an overall sensitivity of -30.5 dBm (BER=10^-9) [including erbium doped fiber amplifiers (EDFA)]     

A 46-ns 1-Mbit CMOS SRAM

A 1-Mb (128 K×8-bit) CMOS static RAM (SRAM) with high-resistivity load cell has been developed with 0.8-μm CMOS process technology. Standby power is 25 μW, active power 80 mW at 1-MHz WRITE operation, and access time 46 ns. The SRAM uses a PMOS bit-line DC load to reduce power dissipation in the WRITE cycle, and has a four-block access mode to reduce the testing time. A small 4.8×8.5-μm² cell has been realized by triple-polysilicon layers. The grounded second polysilicon layer increases cell capacitance and suppresses α-particle-induced soft errors. The chip size is 7.6×12.4 mm²     

⟨110⟩-oriented GaAs MESFETs

GaAs metal semiconductor field-effect transistors (MESFETs) have been successfully fabricated on molecular-beam epitaxial (MBE) films grown on the off-axis (110) GaAs substrate. The (110) substrates were tilted 6° toward the (111) Ga face in order to produce device quality two-dimensional MBE growth. Following the growth of a 0.4-μm undoped GaAs buffer, a 0.18-μm GaAs channel with a doping density of 3.4×10¹⁷ cm^-3 and a 0.12-μm contact layer with a doping density of 2×10¹⁸ cm^-3, both doped with Si, were grown. MESFET devices fabricated on this material show very low-gate leakage current, low output conductance, and an extrinsic transconductance of 200 mS/mm. A unity-current-gain cutoff frequency of 23 GHz and a maximum frequency of oscillation of 56 GHz have been achieved. These (110) GaAs MESFETs have demonstrated their potential for high-speed digital circuits as well as microwave power FET applications     

Tensile-strained GaAsP-AlGaAs laser diodes for reliable 1.2-Wcontinuous-wave operation at 735 nm

Tensile-strained GaAsP quantum wells embedded in AlGaAs large optical cavity structure were investigated at an emission wavelength of 735 nm. 1.2-W continuous-wave operation for 100-μm stripe width diode lasers over 1000 h is reported. Experiments with different stripe widths showed a high stability at an output power of 12-mW/μm stripe widths with degradation rates below 5·10^-5 h^-1, i.e., lifetimes larger than 5000 h could be expected     

The absorption and fluorescence spectra of rare earth ions insilica-based monomode fiber

Rare-earth ions have been systematically incorporated into the cores of silica-based optical fibers, and the absorption and fluorescence spectra have been measured. The results provide basic data for a wide range of possible future fiber-based devices. For specific telecommunications applications, ions that could be useful for sources in the 1.3-μm and 1.5-μm low-loss windows are identified. It is suggested that Er³⁺, Nd³⁺, and Tm³⁺ are the most promising ions for semiconductor pumping with GaAs-based laser diodes     

1.2-μm GaAsP/InGaAs strain compensated single-quantum-well diodelaser on GaAs using metal-organic chemical vapor deposition

We demonstrate here 1.2-μm laser emission from a GaAsP-InGaAs strain compensated single-quantum-well (SQW) diode. This development enables the fabrication of vertical-cavity surface-emitting lasers for optical interconnection through Si wafers. Strain compensation and low temperature growth were used to extend the wavelength of emission to the longest yet achieved on a GaAs substrate in this materials system. The minimum threshold density achieved was 273.4 A/cm² at a cavity length of 610 μm. We have also demonstrated an 1.144-μm lasing wavelength in a 820-μm-long cavity on a GaAs substrate with a strained InGaAs-GaAs SQW laser for comparison using a low-temperature metal-organic chemical vapor deposition growth technique. The threshold current density for a 590-μm-long cavity under CW operation was 149.7 A/cm²     

Concentration effect on gain of Pr3+-doped fluoridefiber for 1.3 μm amplification

The concentration quenching mechanism in Pr³⁺-doped fluoride fiber operating at the 1.3-μm band is investigated. It is confirmed that the cooperative upconversion process causes signal gain saturation with pump power and degrades the gain characteristics of Pr ³⁺-doped fluoride fiber at a concentration of 1000 p.p.m. The reduction in gain coefficient due to cooperative upconversion is almost suppressed at a concentration of 500 p.p.m. A Pr³⁺ concentration of 500 p.p.m. is a practical concentration for the fabrication of efficient Pr³⁺-doped fluoride fiber amplifiers     

A small-size polarization splitter based on a planar optical phasedarray

A device is proposed in which the dispersive properties of an array of bent optical waveguides are utilized for splitting the two polarizations present in the input waveguide. An experimental device for operation at a 633-μm wavelength, with dimensions of 0.6×2.5 mm ², was designed and fabricated using conventional (high-quality) optical lithography. Insertion losses as low as 0.5 dB and far-end crosstalk values of 17-21 dB have been achieved     

Quantum interference control of electrical currents in GaAs

In an earlier publication, preliminary observations of the generation of electrical currents were reported in GaAs and low-temperature-grown GaAs (LT-GaAs) at 295 K using quantum interference control of single- and two-photon band-band absorption of 1.55- and 0.775-μm ultrashort optical pulses. Time-integrated currents were measured via charge collection in a metal-semiconductor-metal (MSM) electrode structure. Here we present detailed characteristics of this novel effect in terms of a simple circuit model for the MSM device and show how the injected current depends on MSM parameters as well as optical coherence, power, and polarization. For picosecond pulse excitation with peak irradiance of only 30 MW/cm^-2 (1.55 μm) and 9 kW/cm^-2 (0.775 μm), peak current densities of ~10 A/cm^-2 at peak carrier densities of 10¹⁵ cm ^-3 are inferred from the steady-state signals. This compares with 50 A/cm^-2 predicted theoretically; the discrepancy mainly reflects inefficient charge collection at the MSM electrodes